Railway train communication system



Dec. 15, 1936. P. N. BOSSART RAILWAY TRAIN COMMUNICATION SYSTEM Filed April 3, 1936 5 Sheets-Sheet 1 Line We're I RTZ Fly.

INVENTOR Paul 1V air/Um.

A'ITORNEY Dec. 15, 1936. BOSSART v 2,064,642

RAILWAY TRAIN COMMUNICATION SYSTEM Filed April 5, 1936 3 Sheets-Sheet 2 .5mllew #3122112! k u INVENTOR H8 119 Paul N Jzr'all. 7 i115 116 7. H16; ATTORNEY.

Dec. 15, 1936. P. N. BOSSART 2,064,642

I RAILWAY TRAIN COMMUNICATION SYSTEM Filed April-5, 1936 3 Sheets-Sheet 3 (T1612 61"? Modalazop I I I l INVENTOR Paul MBoJ Pf 6 1-116 ATTORNEY Patented Dec. 15, 1936 PATENT OFFICE RAILWAY TRAIN oomuomon'non SYSTEM Paul N. Bossart, Cheswicli, Pa., assignor to The Union Switch & Signal Company, Swissvalc, Pa., a corporation of Pennsylvania Application April 3, 1936, Serial No. 723605 31 Claims.

My invention relates to railway 1 train communication systems, and particularly to railway train telephone systems.

The present application is a continuation-inpart of my copending applications, Serial No. 737,076, filed July 26, 1934, for Apparatus for railway train communication systems; and Serial -No. 759,467, filed December 28, 1934,'for Communication systems for railway trains. A feature of my invention is the provision of novel and improved apparatus for railway train communication systems which is operative to transmit communication current along the trackway. A further feature of my invention is the 5 provision of novel and improved apparatus for systems of the type here involved wherewith line wires and other conductors which extend more or less parallel to the track rails are effective I as a communication channel for conveying a communication current along a railway track without it being necessary that the line wire be continuously. near the track rails, such as over the top of a high cut or looping around some obstruction, and without physical connection between the rails and such line wire. Another feature of my invention is the provision in systerns of the type here contemplated of -induc-' tors mounted on a railway train for induction to the track rails of adjacent tracks and other parallel conductors as well as to the rails of the track on which the train is traveling. A still further feature of my invention is the provision of apparatus wherewith a conrmiunication channel is madeavailable for a train traveling on anyone track of a multiple track railway and which channel has a relatively low attenuation of the communication current at the distance equal to the length of an ordinary freight train.

' Again, a feature of my invention is the provision 4 of novel and improved apparatus opeiative'to"v supply communication current to the ails' from a locationv on a railway train by direct coupling. Other features and advantages of my invention will appear as the specification progresses.

I will describe certain forms of apparatus em'- bodying my invention, and'will then point out the novel features thereof in claims.

A train signaling system has been proposed in the United States application for LettersPat ent Serial No. 450 .l35, filed May 6,1930, by L. O. Grondahl for Electric trainsignaling systems, and in which systems the track rails in multiple are utilized as a communication channel for' transmitting communication current between a location on a railway train and a remote location. My present invention may be considered as an improvement on this Grondahl system.

In such systems, the communication current is preferably a modulated carrier current, such as, for example, a side band carrier telephone current. That two-way communication may be accomplished, each location is provided with equipment which consists of transmitting apparatus and receiving apparatus together with circuit means operative to effectively couple each apparatus with the track. rails. 4

When the receiving apparatus of a location is made effective, an electromotive force is created therein in response to the communication current flowing in the track rails, the value of such electromotive force being in accordance with the strength of the current in the rails.

When-the transmitting apparatus of a location is rendered effective an electromotive force corresponding in frequency with the frequency of the communication current is created in the rails adjacent the sending location, and as a result of such electromotive force, current fiow's in the rails in multiple in both directions from the point where such electromotive force is created. The attenuation of such current along the rails is dependent upon the rail to ground or ballast resistance, being relatively high when the ballast resistance is low and being relatively low when the ballast resistance is high. Hence, such current creates along the'rails in each. direction from the sending location a zone of influence which is relatively strong near the sending location and becomes weaker at points distant from the sending location. I have found that a communication current of the order of 8,000 cycles per second flowing in the track rails halves about every 275 feet at locations where the ballast resistanceis' of the order of 3 ohms per 1,000 feet of track with the result that the attenuation of the current may, due to wet ballast and other unfavorable transmitting conditions, be of the order of 10 power in a mile of where it is picked up from the rails is accom plished in part through the medium of line wires and other paralleling conductors disposed along the railway, energy being transferred from the track rails to the line wires and other conductors adjacent the zone' of relatively strong influence and other conductors .back to the track rails throughout adjacent stretches beyond said zone. According to my understanding of the operation, the electrornotive force created in the track rails at the sending location is comparatively large and the current flowing in the rails near the sending location is correspondingly large. The rail current induces an electromotive force in adjacent conductors by virtue of the distributed mutual induction between the rails andv the conductors. The current resulting therefrom in a line wire may not attentuate as rapidly as the original current in the rails with the result that at some distance away from the sending location the current in the line wire is the larger and induces anelectromotive force in the track rails by virtue of the distributed mutual induction. This electromotive force produces a current in the rails which at that location is larger than the original current remaining in the rails. That is, adjacent the zone extending from the sending location and where the rail current is relatively large, energy is transferred to parallel conductors such as a line wire due to the distributed mutual induction of the rails to the line wire. This induction is effective to create an electromotive force in the line wire notwithstanding the line wire may not be continuously near the rails, there ordinarily existing suflicient stretches along such zone of influence where the rails and line wire are in efiective inductive relationship. The electromotive force thus induced in the line wire sets up a flow of communication current in the line wire. The usual line wire is a relatively efficient conductor for such current and hence the attenuation of the current along the line wire is relatively small with the result that at the distance equal to the length of a long freight train the current flow in the line wire is relatively large compared with the communication current transmitted to such distant point through the rails alone. For example, the attentuation of an unloaded bare line wire is of the order of one per cent per mile. At such remote point, an electromotive force is induced in the track rails in response to the current flowing in the line wire due to the distributed mutual induction of the line wire to the rails, such induction being effective adjacent the stretches where the line wire is relatively near to the rails. This latter electromotive force induced in the railssets up a flow of current in the rails in multiple which may be many times larger than the original current in the rails at such remote point.

graph and signal control wires function in this transfer of communication current without interference to the circuits in which they are commonly employed and where several such wires are available each adds to the sum total of the energy transferred, It will be understood, of course, that a line wire which functions only to transmit communication current may be erected if found desirable: Also, tuning devices may be associated with the line wire to increase the flow of communication current. Communication between a location on a train and a remote location consists, therefore, of several stages of energy transfer, namely; .first", from the transmitting apparatus, to the rails: second, induction from the rails to linehwlres and other parallel conductors; third, induction from the line wires and other conductors to the rails of each track of the railway; and fourth, induction from the track rails to the receiving apparatus.

I For a better understanding of my invention, reference may be had to the accompanying drawings in which Fig. 1 is a diagrammatic view of a communication system embodying my invention. Fig. 2 is a view partly diagrammatic and partly perspective showing inductors embodying my invention as preferably mounted on a vehicle of a railway train for inductively transmitting and/or receiving energy. Figs. 3 and 3a are diagrammatic .views of apparatus on a railway train for directly coupling the. transmitting apparatus with the track rails and which apparatus also embodies my invention. Fig. 4 is a diagrammatic view of circuits and apparatus at a location on a vehicle of a railway train wherewith both sending and receiving are accomplished by the inductors of Fig. 2. Fig 5 is a diagrammatic view of circuits and apparatus at a location on a train where sending is accomplished by the apparatus of Fig. 3 or Fig. 3a, and receiving is accomplished by the inductors of Fig. 2. Figs. 6, 7, and 8 are diagrammatic views of apparatus for reducing the impedance of the line wire of Fig. l. Figsq9, 10, and 11 are detail views partly in section of a preferred manner of connecting the sending circuits of Figs. 3 and 3a with journal bearings of the respective vehicles, and for insulating the journal bearings to which connections are made from the associated journal boxes. Fig. 12 is a diagrammatic view showing the parallel connection of the sending circuits of Figs. 3 and 3a with the vehicle wheels to reduce the resistance of the circuits and to provide equal voltage on both track rails.

In each of the several views, like reference characters refer to similar parts.

Referring to Fig. l, the reference characters la and lb designate the track rails of a westbound track RTI, and 2a and 2b designate the track rails of an eastbound track RTZ of a double track railway. The reference character L designates a line wire such, for example, as a. tele-- graph or a telephone wire usually present on a pole line along the right of way. The line wire L may be of any suitable size and material. It will beunderstood that line wire L may be a special wire mounted on the pole line along'the railway tracks. The significant thing to be noted in connection with the line wire L is that due to construction conditions imposed upon a pole line along a railway, the distance between the line wire and the track rails varies, there being stretches where the line wire may be close to the track rails, say less than 30 feet, and other stretches where the line wire may depart several hundred feet from the rails. This condition is illustrated in Fig. 1 by the adjacent sections 33,"

35, and 31, and distant sections 34, 36, and 38. That is to say, due to practical construction, the

line wir'e along the railway track comprises suctlnuously near the track rails but the invention is efiective without special construction to bring the line wire close to the rails.

3| designates the rear vehicle of a railway train occupying the track RTI, and 32 designates the forward vehicle of the train. For example, 3| and 32 may be the caboose and locomotive,

respectively, of a freight train, the intervening cars being omitted and indicated by a dotted line for the sake of clearness. For communication between the caboose 3l and the locomotive 32,

- caboose and locomotive, the caboose will also be equipped with receiving apparatus and the locomotive will be equipped With transmitting apparatus. The operation of the apparatus of Fig. 1 will be taken up after the relationship of the receiving apparatus RA, transmitting apparatus TA, and the line wire L with the track rails of tracks RTI and RTE; and the preferredarrangement of such transmitting and receiving apparatuses are described.

Cl and C2 of Fig. 2 are inductors mounted on a vehicle of a railway train on which communication equipment is installed. These inductors Cl and C2 may take different forms and are here shown as air core coils of relatively largecentral area and constructed to have a relatively low power factor, say, 0.5% at frequencies at the order of 10,000 cycles per second. Fig. 2 illustrates how I would prefer to mount these induc tors upon the caboose of a freight train, the two coils being mounted in a vertical plane on the roof of the caboose one on each side of the cupola. It will be understood, however, that a single inductor placed on one sideof the cupola may be used or the two inductors may both be mounted on the same side of ,the cupola. The inductors Cl and C2 may each consist of many or only a fraction of a turn as desired.

The size and position of inductor coils Cl and C2 of Fig. 2 give relatively large mutual inductance to the track rails of the track occupied by the train. Furthermore, the mutual inductance of these inductors Cl and C2 to the rails of an adjacent track is relatively large since for a vertical coil the maximum inductance to a conductor displaced to the side occurs when the vertical displacement .of the coil is only a trifle greater than the horizontal displacement. That is, the mutual inductance to a conductor displaced to the side is greatest when the coil is mounted at such a height that the angle with the horizontal plane made by a plane through the conductor and the center of the coil is about 45". It will be clear from an inspection of Fig. 2 that the vertical displacement of the inductors CI and C2 mounted on the roof of the caboose with respect to the rails of the tracks RT2 and RT4 is about the same as the horizontal distance,

assuming the usual. 13 foot clearance between track centers is maintained. I have found that a coil-of large central area mounted on a caboose roof as shown in Fig. 2 possesses mutual induccaboose of about the same order as an iron core coil of the same resistance mounted directly over the rail at approximately 6 inch clearance. I have also found that an inductor mounted relatively high on a vehicle possesses inductance to the rails of an adjacent track of the order of 1 to 2 as compared to the inductance of such inductor with the rails of the track occupied. Again, the inductor. coils CI and C2 are in inductive relation with the line wire L-located on a pole line along the right of way. However, due to the distance to the line wire L and to the position of such line wire with respect to the horizontal plane of the inductors CI and C2, their induction to the line wire is small compared with their induction to the track rails and ordinarily may be neglected. With the line wire L brought close to the track and in an effective position, a current in the line wire in phase with such current in the rails adds its effect to that of the rail currents. The inductors CI and C2, when used for sending, induce an electromotive force in the metal body of the caboose which electromotive force is in the same direction as the electromothe noise signal ratio when running is relatively low, much less than the noise signal ratio of inductors mounted just above the track rails.

Consequently, the inductors CI and C2 possess relatively high mutual inductance to the track rails of each of the tracks RTI, RTZ, RT3, and RT4; and due to their position they will induce, when current is supplied thereto, electromotive forces in the several track rails and in the body of the caboose which will produce currents that flow at anyinstant in the same direction in the respective paths. Likewise, a current flowing in multiple in the several track rails and in the body of .the caboose will induce electromotive forces in the inductors which add their effects. Due to construction conditions imposed upon a pole line along a railway, a line wire will ordinarily possess little inductive relationship with these inductors, but

in an effective position will possess mutual inductance with these inductors. To visualize this paralleling arrangement of the track rails with respect to the inductor coils, arrows have been added to Fig. 2. It is clear, this relationship between-the track rails and the inductor coils exists for trains occupying any one of the four tracks. For vehicles other than acaboose the inductor coils Cl and C2 would be mounted on the vehicle at approximately the same height and positions, for example, as they would be mounted on the top at the rear end of a locomotive tender.

Sending circuits effective to supply communication current from train-carried transmitting apparatus to the track rails by direct coupling are disclosed in Figs. 3 and 3a. Referring first to Fig. 3, the reference character V designates a vehicle of a railway train such as, for example, the caboose of a freight train and on which vehicle communication equipment is mounted, the transmitting apparatus being indicated conventionally at TA. It is deemed sufficient for this application to point out that when the transmitting apparatus TA is rendered active, a communication current is supa line wire when brought close to the track and plied to the primary winding 9 of an output transformer Tl, the secondary winding 8 of which is interposed in a sending circuit that includes the wheels 4 and at the opposite ends of the caboose, and the track rails between these wheels, connection with the wheels being prefconstruction being disclosed in Figs. 9, 10, 11,

and 12. One terminal of the secondary winding 8 of the output transformer TI is connected with the journal bearing 80 (Figs. 9, and 11) of wheel 5 by a flexible insulated conductor 6, connection to the bearing 88 being made by means of a flat terminal lug H2 secured to the end of the bearing 89 by two screws H3 tapped into the bearing, and the flexible conductor 6v being carried through the wall of the journal box JB by any convenient bushing. As shown in Fig. 12, there is a parallel connection 6a from conductor 6 to the journal bearing of the wheel Ed at the other end of the same axle. Such parallel connections are made to the bearings at both ends of the axle to reduce the contact resistance between the bearings and the axle, and between the wheels and the rails, and to maintain the same voltage on both track rails. Connection from the other terminal of the secondary winding 8 is taken over conductors 8| and 82 to the extreme lefthand end of the Caboose, then vertically by conductor 83 to a point about 6 inches above the caboose roof, along one end of the caboose roof by conductor 84, conductor 85 over the cupola without exceeding existing clearances, conductor 85 along the other end of the roof, downwardly by conductor 81 at the extreme righthand end of the caboose, conductor 88, and flexible conductor 1 to the journal bearing of the wheel 4, the connection of flexible conductor with the journal bearing of wheel 4 being the same as that described for connectingthe flexible conductor 6 to the journal bearing of wheel 5. The conductor 1 is provided with a parallel connection la (Fig. 12) to the journal bearing of the wheel 4a at the other end of the same axle to reduce the resistance of the circuitand to assure the same voltage is apcurrent flows in the rails in each direction from the caboose and returns through the ground path as illustrated by broken lines in Fig. '3. 1

The current flowing in the rails adjacent the caboose is relatively large but" diminishes in value as the distancewfrom the caboose is increased. This diminishing value of the current is illustrated by arrows placed on Fig. 3. It will be apparent that due to such current a zone of influence extending in both directions from the caboose is established and which zone moves along with thejcaboose and the influence of which becomes less as the distance from the caboose becomes greater.

The important thing is to produce the maximum voltage along the track rails for a given power output of the apparatus TA; Thevoltage E depends upon two factors, the current flowing in the rails from wheels 4 to 5, and the impedance of the rails between the points of contact. Consequently, the remaining portion of the sending circuit outside of the rails should be of low resistance. For this reason, the conductors 82, 83, 84, 85, 86, 81, and 88 are constructed of copper pipe, say one inch size. Because of skin efiect, there is no need to have these conductors solid. This copper pipe also provides a conductor having the desired mechanical strength. These conductors are insulated as indicated at 99 in any suitable manner from the metallic parts of the caboose. The other-factor, impedance of the rails between wheels 4 and 5, depends in part upon the length, and hence it is desirable to connect to the wheels furthest apart. The rail impedance is made up of resistance and reactance, the latter being many times the larger of the two factors at the frequency of the communication current used. The inductive reactance depends upon the distance the return portion of the circuit is away from the rail, increasing neglecting end effects with the ratio logarithm of the distance to the return portion of the circuit divided by the radius of the conductor used. It is clear that with the sending circuit constructed as described above, the return portion of the circuit over the roof of the caboose is removed as far as possible from the track rails. As will appear hereinafter, the return portion of the sending circuit when carried far away from the track rails eflects a further advantage since the current in the return portion of the circuit flows in the same direction as the current in the rails beyond the caboose. Arrows have been added to Fig. 3 to visualize the direction of the current at an instant the voltage E is of the polarity indicated by the plus and minus signs.

In order to have as much current in the rails as possible, shunt paths from wheel 4 to wheel 5 should be avoided. One shunt path that might occur would be. from the journal bearings through the journal boxes and body of the caboose. Current is prevented from flowing through such shunt path by insulating the. journal bearings from the wedge which holds it in the-journal box and from the-journal box itself. Referring to Figs. 9, 10, and 11, the reference character 89 is the axle, a shoulder 98 being formed thereon to prevent the bearing 80 from working past the end of the axle. 9| is the iron wedge which goes between the bearing 89 and the journal box JB, the wedge 9L engaging the top of the journal box at 92 to prevent its moving outward. Bearing 80 has a collar 93 which extends up back of the wedge 9! so that the wedge cannot move inward. The bearing 80 is prevented from moving inward by the side projections 94 and 95 engaging'opposing projections of the journal box JB. The above construction is-that of standard practice. To insulate the journal bearing 80 from the wedge 9| and from the journal box JB a sheet of insulation 95 is provided. This insulating sheet may be of anysuitable material such asflber and is formed to fit over the bearing 80, as shown in Fig. 11, covering the entire bearing area between the bearing and the wedge. The fiber sheet 96 circuit extends by conductor is turned up over the .collar 93, as shown in Fig. 10. To prevent the bearing 80 from touching the journal box at its projections 94 and 95, the fiber sheet is turned down, as shown at 91 and 98. It is thus seen that the bearing 80 does not make metallic contact to the journal box JB direct or through the wedge 9| which holds it in place. I have found that such insulation is easily installed and is effective. It follows that with the bearings for the wheels 4, 4a, 5, and 5a of the caboose insulated in the manner explained above, a shunt path from the journal bearings through the journalboxes and the body of the caboose is avoided, and substantially all of the current follows the path through the wheels and track rails. When the brakes are applied, there is a possibility of a shunt path through the brake rigging, but this occurs after the current is in the wheels which are in direct contact with the rails and such shunt path is of relatively high resistance.

Fig. 3a discloses a similar sending circuit applied to a locomotive. n the locomotive, a convenient place for housing the communication equipment is on the top of the rear end of the tender as indicated at EH. One terminal of the secondary winding I00 of an output transformer T3, the primary winding IOI of which is connected with the transmitting apparatus of the locomotive, is connected to conductor I02 which extends to the rear of the tender, thence by conductor I03 down the back of the tender and then by flexible conductor I04 to the journal bearing of the rear wheel III of the'tender, connection of conductor I04 to the journal bearing being in the manner shown in Figs. 9, 10 and 11.

The conductor I04 is provided with a parallel connection to the journal bearingat the other end of the same axle similar to that disclosed in Fig. 12 for conductors 6 and 1. Starting at the other terminal of the secondary winding I00, the I05 supported above the tender side wall, flexible removable coupler I06 between the tender and locomotive, conductor I01 supported along the roof of the locomotive cab along the locomotive boiler by conductor I08 which when properly insulated may serve as a secondhand rail parallel to the same axle. This circuit is preferably constructed as .far as possible out of copper pipe similar to I the sending circuit of the caboose and insulated from the metallic parts of the locomotive. It will be understood, however, that my invention is not limited to the use-of copper pipe for these 1 sending circuits and other conductors may be used if found desirable. It is clear that the locomotive sending circuit as described above possesses the desirable characteristics discussed for the sending circuit on the caboose.

It has been proposed for systems of the type here under consideration to modulate a carrier current with voice frequencies for telephoning, and to modulate the carrier bya single predetermined voice frequency for calling and code signaling. The receiving apparatus at each location is normally active and in .circuit ready to receivea message from remote location at any time, but the transmitting apparatus at each location is normally inactive and is energized vention.

and placed in circuit only during the sendingv ofcurrent from that location. To reduce noise and to provide selectivity, the receiving circuit may be sharply tuned to the single frequency which corresponds to the calling frequency. The

tuning of the receiving circuit is, for telephoning, broadened for the reception of a band of frequencies of a width equal-to the desired voice frequency range. For code signaling, the send-' ing location sends impulses of the calling fre-- quency in accordance with a prearranged code, the receiving circuit at the remote location being retained at its sharply tuned condition. To fix theideas I shall assume that a band of voice frequencies extending from 600 cycles to 1800 cycles per second for telephoning is desired, the calling frequency is 800 cycles per second, a carrier of 7000 cycles per second is employed and single side band transmission is contemplated, the upper side band being transmitted. It follows that during telephone communication a band of frequencies extending from 7600 to 8800 will be transmitted and for calling and code communication the frequency will be 7800 cycles. It will be understood, of course, that my invention is not limited to these specific frequencies and other frequencies may be chosen.

The transmitting apparatus will ordinarily include a microphone, a generator of carrier current, means for modulating the carrier with frequencies corresponding to the voice impulses produced in the microphone, calling means operative to produce a frequency equal to the carrier modulated by the predetermined voice fre modulator for reproducing the audio frequencies of the modulated carrier, an audio frequency amplifier, filters for suppressing frequencies outside the desired band, and a loudspeaker. The specific structure for such amplifiers, modulators, and demodulators forms no part of my present invention, and these devices will be, re,

ferred to in the present description only insofar as it is necessary for the understanding of my invention. The inductor coils of Fig. 2 are effective to both send and receive energy and, hence, one embodiment of the invention will include the use of the inductor coils for both sending and receiving. A second embodiment of the invention will employ the sending circuitsof Figs. 3 and 3a and the inductors of Fig. 2 for receiving. In Fig. 4, a preferred form of circuits and apparatus for employing the inductor coils for both sending and receiving is disclosed. In Fig. 5, a preferred form of circuits and apparatus for sending by the circuits of Figs. 3 and 3a. and receiving by the inductor coils of Fig. 2 is disclosed.

Referring to Fig. 4, the microphone is indicated by the reference character M, while the carrier generator, modulator, generator and power amplifier are indicated conventionally at TA, since, as stated above, these latter devices form no part of my present in- The microphone M is preferably carried during non-communicating periods in a rack, not shown, and out of which it may be lifted when it is desired to establish a telephone conversation in order that it may be brought close to the person speaking. To facilitate the handling of the microphone M, it is mounted on a handle I5 which is adaptable to be manucalling current ally operated to any one of three positions which I shall term "normaY, communicating, and calling, these three positions being indicated by dotted lines in the drawing. As shown schematically, two circuit controlling contacts l6 and BI are operatively connected with the handle l5 and are moved to the three positions designated by the numerals 1, 2, and 3, in response to the normal, communicating and calling positions,-respectively. A push button I! is also mounted on the handle I5, the contact member l8 of which is adapted to make engagement with a contact I9 when the push button is depressed and to break engagement therewith when the push wtton is released. A circuit controlling contact 20 is associated with the microphone M and is biased by its own spring action to make engagement with a stationary contact 2| but is normally held out of engagement therewith through the medium of an insulated member 22 mounted on the microphone M, the arrangement being such that with the microphone M placed in the rack, the member 22 forces the spring 20 to the left in the drawings and out of engagement with the contact 2|, but that with the microphone M removed from the rack, that is, moved to the right in the drawings, the member 22 disengages the contact 20 and that member springs into engagement with contact 2| to complete the connection therethrough. It will be noted that the handle l5 may be operated to any' one of its three positions with the microphone remaining in the rack, as well as when it is lifted out of the rack.

The microphone M is connected with the inin the wire l2, and a second front contact '|576 of the relay being interposed in wire i3. The circuit for rendering the transmitting apparatus active to supply a calling frequency current is shown completed by the'contact 6| being moved to its No. 3 position to connect the two wires 62 and 63. It is deemed suflicient for this description to say that frequencies corresponding to voice frequencies developed in the microphone will be applied to the carrier, which in this instance is of 7000 cycles per second, for modulat-' ing the carrier, the carrier and the lower side band will be suppressed and the upper side band will be amplified to a relatively high energy level and supplied to the winding M of the transformer T, the winding l4 being in turn effective to induce electromotive forces of corresponding will be amplified to a relatively high energy level and supplied to the winding I4 and in turn supplied to the transmitting circuits.

The equipment of Fig. 4 includes a directional relay DR and a tuning relay R both of which are shown as direct current neutral relays adaptable of being energized by direct current from any convenient-source such as a battery, not shown. The directional relay DR is provided with two energizing circuits both of which are easily traced and one of which includes the No. 2 position of the contact l6 and the push button I! depressed, and the other of which includes the No. 3 position of the contact I6 only. That is to say, the directional relay is deenergized under the normal position of the microphone handle l5, and is energized when the handle I5 is moved to the communicating position and the push button I! is depressed, and also when the handle I5 is moved to the calling position. The tuning relay R is provided with two simple energizing circuits one of which includes the contact 20-2I, and the other of which includes the contact 23 of a common spring return push button 24. Hence, the tuning relay R is normally deenergized and is energized whenever the microphone M is taken out of the rack and the contact 20-2l is closed, and may also be energized while the microphone M remains in the rack by depressing the push button 24. The function of the tuning relay R and the directional relay DR will appear later in the description.

In Fig. 4, the inductor coils Cl and C2 are connected in parallel across the winding 61 of the transformer T by either one of two circuits, the first circuit being traced from the top terminal of the coils over a back contact 65-66 of the tuning relay R, condenser 68, lower portion of the winding 61, and wire 69 to the lower terminals of the inductor coils. The parts of this circuit are so proportioned and adjusted as to tune the circuit to resonance at the calling frequency of 7800 cycles and to give the circuit a power factor of say 1.0%. At such time as the tuning relay R is energized to lift the contact finger 65 out of engagement with the back contact 66 and into engagement with the front contact 10 the inductor coils Cl and C2 are connected across the full portion of the winding 61 through a condenser II. The condenser 'H and the full portion of the winding 61 are so proportioned as to tune the circuit to resonance at about the mid-voice frequency and to raise the power factor of the ,circuit to about 5.0%, and, hence, make the circuit effective to pass a band of frequencies equal to the desired voice frequency range, which in this instance extends from 7600 to 8800 cycles.

Currents supplied by the coils Cl and C2 to the winding 61 of the transformer T will induce electromotive forces of corresponding frequencies in the winding M of that transformer and which winding is normally connected with the input of the receiving apparatus RA through the bandpass fllter Fl, the back contacts !5'l2 and 11-43 of the directional relay DR being interposed in the connection. The output side of the receiving apparatus RA is connected with a loudspeaker LS.

It follows that with relays R and DR both released the inductor coils Cl and C2 are included in a low power factor circuit sharply tuned to the calling frequency, and the current supplied by these inductor coils to the winding 61 of the transformer T will be passed to the input of the receiving apparatus over back contacts of the directional relay and through ahaving a relatively high power factor and tuned to resonance at the mid-voice frequency, and the telephone current will be effectively replied to the inductor coils Cl and C2 for inducing an electromotive force in the traflic rails and the neighboring paralleling conductors, the

coils being tuned to the calling frequency when the tuning relay R is released and tuned to pass the voice frequency band when the tuning relay R is picked up. In Fig. 4,'the inductors Cl and C2 are shown connected in parallel. It is clear, however, they may be connected inseries winding 3 of the transformer Tl being interposed in a sending circuit such as described in Fig. 3. The input of the amplifier-demodulator AD of the receiving apparatus RA is connected with inductor ClC2 through a band-pass fil-. ter BPF and the output of this amplifier-demodulator is supplied to a transformer T2 and, in turn, to the loudspeaker LS. A power unit PU consisting of two motor-generators or dynamotors DMI and DM2 is provided. The motor 43 of the motor-generator DMI is constantly supplied with power from any convenient source of current such as a battery, not shown, the two terminals of the source being indicated at B32 and N32. The motor 64 of the motor-generator DM2 is normally inactive and is supplied with current from the source B32N32 when the relay DRI is energized and its front contact 44 is closed. The generator 45 of motor-generator DMI is connected with the plate circuits of the tubes for the amplifier-demodulator AD of the receiving apparatus over a circuit including positive terminal of generator 45, wire 46, back contact 41 of relay DRI, wire 48, plate circuits of the tubes of the amplifier-demodulator and thence over wire 49 to the negative terminal of the generator 45. Energization of the relay DRI in a manner to be shortly described to open its back contact 41 and close its front contact 50 transfers the generator 45 to the of the amplifier-modulator AM and thence by Wires 52 and 49 to the negative terminal of generator 45. When the relay DRI is energized and its front; contact 53 is closed, the generator 45 of motor-generator DMI 'and the generator 54 of motor-generator DM2 are connected in series for supplying voltage tothe plate circuits for the tubes of the power amplifier PA of the transmitting apparatus. This circuit is from the positive terminal of generator 45, wire 46, front contact. 53 of relay DRI, wire 55, generator-54, wire 56, plate circuit for the power tubes,and

a current set up in these latter rails.

' low. Third, nduction from the line wire L thence by wires 52 and 49 to negative terminal of generator 45. The relay DRI is provided with an energizing circuit similar to that described for the relay DR of Fig. 4, and which circuit is controlled by the push button I! and the contact l6 associated with the microphone handle l5.

Referring again toFig. 1, the transmitting apparatus TA on thecaboose 3| is arranged for sending current by the circuit of Fig. 3, and the receiving apparatus RA on the locomotive is arranged to pick up energy through the medium of the inductor coils of Fig. 2. Assuming the train'crew in. the caboose desires to telephone to the crew on the locomotive, the equipment in the caboose is manipulated to render the transmitting apparatus effective to supply telephone current to the track rails. As a result of such current supplied to the rails at the caboose, current flows in the rails of track RTI in both directions from the caboose. Along the zone extending from the caboose, induction of the rails to the line wire L induces an electromotive force in the line wire. This transfer'of energy is illus trated in Fig. l by broken lines with arrows added to indicate that the energy transferred is from therails; to the line. Itis noted that this transfer of energy from the rails to the line wire is effected notwithstanding the fact that section 34 of the line wire L adjacent the caboose is distant from the rails. This is because the communication current in the rails is still at a relatively high level opposite the adjacent sections 33 and 35. The electromotive force induced in the line wire L creates a flow of current in the line wire in both directions. attenuation of this current in the line wire is relatively low so that at a distant point such as section 31 adjacent the locomotive 32, the current in the line wire induces an electromotive force in the rails la and lb of track RTI and also in the rails 2a and 2b of the track RT2. This energy transfer is illustrated by dotted lines with arrows placed thereon to indicate that the transfer is from the line wire to the rails. The electromotive force thus induced in the rails ad- 'jacent the section 3'! of the line wire causes a current to flow in the rails in multiple and which current is relatively large with respect to the original current remaining in the rails la and lb. The inductor on the locomotive 32 inductively receives an electromotive force the value of which is the sum total of that produced by the current in the rails la and lb and also by the current in the rails 2a and 2b. It is'to be noted that the currentsupplied to the rails la and lb at the caboose 3l may induce an electromotive force in the. rails of the adjacent track RT2 and The attennation of such current in the rails 2a and 2b is relatively large due to the ballast resistance and is negligible adjacent the locomotive 32. It follows that the transmission of communication current from the caboose to the locomotive consists of four stages of energy transfer. First, transmitting apparatus TA to the track rails to create current which flows in the rails la and lb, and which current is relatively large close to the caboose but which has a relatively large attenuation due to the ballast resistance. Second, induction from the rails along this zone of relatively large rail current to the line wire L to cause current to flow in the line wire and the attenuation of which current is relatively The i the track rails of both tracks at locations distant from the caboose which causes a rail current larger than the original current remaining in the rails at such distant locations. Fourth, induction from the rails to the receiving inductor mounted on the locomotive and which inductor is positioned for inductive relationship with the rails of the adjacent track as well as with the rails of the track occupied. It can be shown thatat a locality where the ballast resistance is about 6 ohms per thousand feet of track, the line wire increases the received current about 14 times in the case of a freight train of 100 cars.

It is to be noted that with the caboose of the train of Fig. 1 provided with the sending circuit of Fig. 3, the current flowing in the return portion of the sending circuit along the caboose roof will flow in the same direction as that of the rail current beyond the caboose and opposite in direction to that flowing in the rails between the caboose wheels. This being so, the mutual induction effected by this return portion of the sending circuit on the line wire L will oppose the induction eflected by the rail portion of the sending circuit on the line wire, and will be the larger of the two since the return portion is usually closer to the line wire. Although the rail currents beyond the caboose are much' smaller than the current in the return portion of the sending circuit, yet because of their much longer exposure to the line wire, the effect of the current in the rails will be the larger. It is clear that with the locomotive 32 equipped with the sending circuit of Fig. 3a. and the caboose equipped with inductor coils, communication current will be transferred from the locomotive to the caboose through the medium of the line wire L in a. manner similar to that described above. Hence, if the caboose and locomotive are both provided with the equipment of Fig. 5 and the two train crews operate their respective equipments to the sending and receiving conditions, telephone communication between the caboose 3| and the locomotive 32 may be accomplished, the efiective communication channel being over the line wire L. 'Furthermore, it is apparent that with the caboose 3i and the locomotive 32 both equipped with the equipment of Fig. 4 communication between these two locations may be accomplished with the line wire L serving as the effective communication channel. Best results have been found to occur when the inductor coils are mounted in the position of maximum induction to the track rails, and'direct induction with the line wire is negligible. It is clear that line wire L will serve as an effective communication channel for a train operating on track RT2.

Figs. 6, '7, and 8 disclose apparatus effective to compensate the impedance of the line wire L for the communication current. The characteristic impedance for an open wire line wire of No. 10 gauge copper. wire strung about 10 feet off the ground, a leakage of about one megohm and a distributed capacitance of about .002 microfarad per 1000 feet, will be approximately 5'75 ohms at 8000 cycles. The propagationconstant will be of such value that the current will lose only about one-half of one per cent of its value per mile. pedance and hence increase the flow of communication current in response to the electromotive force induced at any point of the line wire and to maintain the propagation constant To reduce the characteristic im-' at a value such that the attenuation of the current is less than one-half at a distance equal to the length of an ordinary freight train, the tuning devices of Figs. 6, '7, and 8 are useful. In Fig. 6, these tuning devices each consists of a shunt condenser and a series condenser. At spaced locations the condensers 25, 26, and 21 are serially interposed in the line wire L, one at each location. Condensers 28, 29, and 30 are connected between the line wire L and ground at the locations of the condensers 25, 26, and 21, respectively. It can be shown mathematically that with the line wire L of Fig. 6 an open wire of No. gauge copper wire, condensers 25, 26, and 21 each of about 0.4 microfarad, condensers 28, 29, and 30 each of about 0.64 microfarad, and the tuning devices spaced about one mile apart, the reactance of the line wire L is tuned out and the characteristic impedance is substantially 20.5, 27.5, and 35 ohms at 7600, 8450, and 9300 cycles, respectively. The propagation constant at these frequencies is such that the currents have a value of about 50, 68, and '75 per cent of the original value at a distance of one mile. In other words, the tuning devices of Fig. 6 are effective to reduce the average characteristic impedance of the line wire to about 28 ohms and approximately two-thirds of the communication current is left at a distance of one mile from the point of induction.

The serial condensers 25, 26, and 21 of Fig. 6 may be omitted leaving the tuning devices to consist of the shunt'condensers 28, 29, and 30 only. With such an arrangement and with each of the condensers 28, 29 and 30 of about 0.63 microfarad and spaced along the open wire line L about every 1670 feet, the characteristic impedance of the line'will be about 32 ohms at 8000 cycles. The propagation constant for the line wire will be such that the current will be about 92% of its original value at a distance of one mile from the point of induction.

In Fig. '7, tuning devices consisting of a re- Sister and a condenser are provided at spaced locations along the line wire, the resistor being interposed between the line wire and ground and the condenser being serially connected with the line wire. It can be shown mathematically that with the line wire of Fig. 7 of No. 13 gauge copper wire, resistors H5, H6, and II! each of about 22 ohms, condensers I I8, H9, and I20 each of about 0.36 microfarad, and the tuning deshunt condenser is at the mid-terminal of thetwov series condensers as will be readily understood by an inspection of Fig. 8.

I have found that tuning devices such as disclosed in Figs. 6, '7, and 8 and connected with an open wire line at selected points are effective to increase the flow of communication current and still maintain an attenuation such that over 50% of the current remains at a distance of one mile from the point of induction.

The propagation 1. In combination with railway train-carried communication equipment including a signaling.

device responsive to an-alternating signaling current, an air core inductor of relatively large central area, said inductor mounted in a vertical plane on the roof of a vehicle of the train for inductively receiving electromotive forces due to an alternating signaling current which flows in the trafiic rails of the track occupied by the a train and in the neighboring conductors parallel to said rails in multiple, and circuit means for connecting the inductor with the ,communica-' tion equipment for actuating the signaling device in response to the electromotive forces induced in said inductor.

2. In a railway communication system comprising train-carried receiving apparatus ineluding a signaling device responsive to alternating current; a communication channel including the traffic rails of the track occupied'by a train, the trafiic rails of the tracks adjacent thereto, and line wires parallel therewith; and transmittingapparatus remote from the receiving apparatus including a source of alternating signaling current effective to supply to said channel current which flows in the several conductors thereof in parallel; a first and a second air core inductor 'of relatively large central area mounted on a vehicle of a train above the body of the vehicle, said inductors placed in a vertical plane one'in advance of the other for inductively receiving electromotive forces due to vthe signaling current flowing in the several conductors of the channel, and circuit means forconnecting said inductors with the receiving apparatus for actuating the signaling device in response to the combined energy of the electromotive forces induced in the inductors.

3. In combination with railway train-carried communication equipment including transmit- "cupied and in neighboring conductors parallel to said rails when said inductor is connected to the transmitting apparatus, and to inductively receive electromotive forces due to modulated carrier current flowing in said rails and in the neighboring parallel conductors when said inductor is connected to the receiving apparatus, and train-carried control means to selectively .connect said inductor either to the transmitting apparatus or to the receiving apparatus.

zontal magnetic field transverse to the track for inductively receiving electromotive forces due to an alternating signaling current which flows in each of the rails of said. two tracks in parallel, and circuit means for connecting the inductor with the communication equipment for actuating the signaling device in response to the electromotive forces induced in said inductor.

5. In combination with railway train-carried communication equipment including a signaling device responsive to an alternating signaling current, an inductor mounted on avehicle of a train above the body of the vehicle and at a height above the track substantially equal to the horizontal distance between the track occupied by the train and an adjacent track, said inductor positioned to link a horizontal magnetic field transverse to the traclrfor inductively receiving electromotive forces due to an alternating signaling current which flows in the train body and, in each of the rails of said two tracks in parallel and which forces add their effects, and circuit means for connecting the inductor with the communication equipment for actuating said signaling device in response to the electromotive forces induced in said inductor.

6. In a railway communication system comprising train-carried receiving apparatus including a signaling device responsive to alternating current; a communication channel including the traffic rails of the track occupied by a train, the trafiic rails of the tracks adjacent thereto, and

line wires parallel therewith; and transmitting apparatus remote from the receiving apparatus including a source of alternating signaling current effective to supply to the channel current which flows separatelyin each of the several conductors thereof; in combination with the above instrumentalities a train-carried inductor mounted on a vehicle of the train at a height substantially equal to the horizontal distance between the track occupied by the train and an adjacent track, said inductor mounted in a plane to link a horizontal magnetic field transverse to the track for inductively receiving electromotive forces due to the signalingcurrent flowing in the several conductors of the channel which forces, are additive in their effects, and circuit means for connecting the inductor with the receiving apparatus for actuating the signaling device in response to the electromotive forces induced in the inductor.

7. In a railway communication systemcomprising train-carried receiving apparatus includ-' ing a signaling device responsive to alternating current; a communication channel including the trafllc rails of the track occupied by a train, the traiiic rails of the tracks adjacent thereto, and line wires parallel therewith; and transmitting apparatus remote from the receiving apparatus including a source of alternating signaling current effective to supply to the channel current which flows separately in each of the several conductors thereof; in combination withthe above instrumentalities a train-carried air core inductor of relatively large central area mounted on a vehicle of a train above the body of the vehicle and in a verticalplane for inductively receiving electromotive forces dueto the signaling current flowing in the several conductors of the channel and which forces are additive in their effects, and circuit means for connecting the inductor with the receiving apparatus for actuating the signaling device in response to the electromotive forces induced in the inducton 8. In combination with railway train-carried telephone equipment including transmitting apparatus capable oi supplying a carrier telephone current and receiving apparatus capable of reproducing the audio frequencies 01' a carrier telephone current, an inductor mounted on a vehicle oi the train above the body of the vehicle and positioned in a plane to,link a' horizontal magnetic field transverse to the track-tor induction to the body of the vehicle and to the traillc rails of the track occupied by the train and the trafllc rails or an adjacent track,'a first circuit means to connect said inductor with the transmitting apparatus for. inductively supplying a telephone current which flows in the train body and in the traillc rails of said tracks in parallel, a second circuit means to connect the inductor to the receiving apparatus for inductively receiving electromotive forces due to a carrier telephone current flowing in the train body and in the trafllc rails of said tracks in parallel, and manually controlled means for governing said first and second circuit means.

9. A railway communication system comprising, a train including two spaced vehicles, means on one vehicle including a source of communication current and a circuit coupled to the track rails to cause communication current to flow in the rails in multiple from said vehicle, means on the other vehicle including a signaling device responsive to the communication current and a circuit coupled to the track rails for receiving an electromotive i'orce due to communication current flowing in the rails in multiple, and a line wire disposed along the railway and so positioned with respect to the rails that the communication current flowing in the rails at said one vehicle induces current in the line wire by virtue of the the other vehicle including a signaling device responsive to the communication current and a circuit coupled to the track rails for receiving an electromotive force dueto communication current flowing in the rails in multiple, and a line wire disposed along the railway and so positioned with respect to'the rafls that communication current is transferred from the rafls to the line wire adjacent said one vehicle solely by virtue of the distributed mutual induction between the rails and the line wire and is transferred from the line wire back to the rails adjacent said other vehicle solely by virtue of the distributed mutual induction between the line wire and the rails in multiple.

11. A railway communication systemcomprising, a train including two spaced vehicles, means on one vehicle including a source of communication current and a circuit coupled to the track rails to cause communication current to flow in the rails in multiple from said vehicle, means on the other vehicle including a signaling device'responsive to the communication current and a circuit coupled to the track rails for receiving an electromotiv'e force due togximmunication current flowing in the rails in multiple, and a line wire disposed along the railway and so posigreater than the original current in the rails at oned with respect to the rails that communication current is transferred from the rails to the line wire adjacent said one vehicle by virtue of the distributed mutual electromagnetic induction between the rails and the line wire and is trans- 6 i'erred from the line wire back to the track rails adjacent said other vehicle by virtue of the distributed mutual electromagnetic induction between the line wire and the rails in multiple.

12., A railway communication system comprising, means at one location along the railway including a source of communication current and a circuit coupled to the track rails to cause communication current to flow in the rails in multiple in both directions from said one location, said rails characterized by relatively high attenuation for the communication current, a line wire extending along the railway and so positioned with respect to the rails that the communication current induces current in the line wire by virtue of the distributed mutual induction between the line wire and therails adjacent said one location, said line wire characterized by a relatively low attenuation for the communication current whereby the current in the line wire induces current back in the rails at locations remote from said one location by virtue of the distributed -mutual induction between the line wire and the track rails and which latter current is 30 such remote locations, and means remote from said one location including a signaling device responsive to the communication current and a circuit coupled to the track rails for receiving an electromotivei'orce due to said latter communication current flowing in the rails.

' 13. A railway communication system comprising, a train including two spaced vehicles, transmitting apparatus located on oneof the vehicles including a source of communication current and .a circuit coupled to the track rails to cause communication current to flow in the rails in multiple in both directions-from said vehicle,

said rails characterized by relatively high attenuation for the communication current whereby a zone of influence extends from said vehicle in both directions with diminishing intensity, a line wire extending along the railway and so positioned with respect to the track rails that the communication current flowing in the rails 50 induces current in the line wire by virtue of the -mutual induction between the rails and the line wire adjacent said zone, said line wire characterized by relatively low attenuation for the communication current whereby the line current is eflective toinduce current in the rails adjacent the other vehicle by virtue of the mutual induction between the line wire and the rails and which latter current is greater thanthe original current remaining in the rails at 0 .said other vehicle, and receiving apparatus losource and a sending circuit coupled to the rails to cause a communication current-to flow in the rails in multiple in both directions Irom said vehicle to induce an electromotiveiorce in the 7 line wire by virtue of the distributed mutual induction between the rails and the line wire adjacent such of its sections close to the rails in the vicinity of said vehicle for causing communication current to flow in the line wire, said line wire characterized by attenuation to the communication current relatively low compared to the attenuation of the rails to the current whereby the line current induces an electromotive force in the rails by virtue of the distributed mutual induction between the rails and the line wire adjacent its sections close to the rails remote from said first vehicle to cause communication current to flow in the rails which is greater than the original current at such remote distance from said vehicle, and receiving apparatus on a second railway vehicle remote from said first vehicle and including a signaling device responsive to the communication current and a circuit coupled to the rails.

15. A railway communication system comprising, a line wire disposed along the railway which due to construction conditions consists of sections relatively close to the track rails and other sections relatively far from the track rails, a train including two vehicles spaced relatively far apart, transmitting apparatus on one of the vehicles including a source of communication current and a circuit coupled to the track rails 'to cause communication current to fiow in the rails in multiple in both directions from said one ,vehicle, said current eflective to transfer communication current to the line wire by virtue of the mutual induction between the rails and therelatively close sections of the line wire in the vicinity of said one vehicle, said line communication current effective to transfer current to the rails by virtue of the mutual induction with the track rails.

16'. A railway communication system comprisin a railway track, a train to travel on said track, means located on a vehicle or the train including a source of communication current and a circuit coupled with the track rails to cause communication currentto flow in the rails in multiple in both directions from the vehicle, a

*line wire disposed along said railwayior distributed mutual induction to. the track rails for inductively receiving an electromotive force due to the current flowing in the rails to cause a corresponding current to flow in the line-wire, and receiving apparatus remote from said vehicle including a signaling device responsive to said communication current and a circuit eflectively coupled with said line wire.

1'7. A railway communication system comprising, a railway track, a train to travel on said track, means located on a vehicle of the train rail due to communication current flowing in the line wire for causing communication current to flow in the two rails in multiple, and means remote from said vehicle including a source of communication current and a circuit effectively coupled with the line wire for causing communication current to' flow in the line wire.

18. A railway communication system comprise ing, transmitting apparatus located on one vehicle of a train and including a current source and a sending circuit efiectively coupled to the track rails to cause a communication current to flow in a first rail circuit consisting of the two rails in multiple to each side of-the vehicle and ground return, receiving apparatus located on another vehicle of thetrain spaced apart from said one vehicle and including a signaling device responsive to the communication current and a receiving circuit eilectively coupled to the track rails to receive anelectromotive force due to communication current flowing in a second rail circuit consisting of the two rails in multiple to each side of said other vehicle and ground returmand a line wire extending along the railway for distributed mutual induction to the rails for inductlvely receiving an electromotive force due tc the current in the first rail circuit to cause communication current to flow in the line wire which induces an electromotive force in the rails to cause communication current to flow in said second rail circuit.

19. A railway communication system comprising, a multiple track railway, transmitting apparatus located on one vehicle or a train occupying' one of said tracks and operative to cause a communication current to flow in the rails of that track in multiple in both directions from said vehicle, said rails characterized by relatively high attenuation for such current,a' line wire disposed along'said railway in an inductive relation with the rails of said tracks for inductively receiving an electromotive force due to such current in the railsoi' said one track to cause communication current to -flow in the line wire, said line wire characterized by relatively low' attenuation for the communication current whereby theline current induces an electromotive force in the rails of each track at points remote from said one vehicle and which electromotive force causes cur-- rent to flow inthe rails of all the tracks in multiple, and receiving apparatus located ona second vehicle of the train remote from said one vehicle including a signaling device responslve to such communication current and an inductor, and said inductor mounted in a vertical plane above the body of the vehicle in an inductive relation with the rails of the adjacent tracks as well as with the. rails of the track occupied to actuate said signaling device by the electromotiveforce received due 'to the current inthe rails 01' all the tracks in multiple.

20. A railway communication system comprising, a multiple track railway, transmitting apparatus located on one vehicle of a train 0ccupying one of said tracks and operative to cause a communication current to flow in the rails of that track in multiple in both directions from said vehicle, said rails characterized by relatively high attenuation for such current, a line wire disposed along said railway in an inductive relation with the rails of said tracks for inductively receiving'an electromotive force due to such current in the rails of said one track to cause communication current to flow in the line wire, said line wire characterized by relatively low attenuation for'the communication current whereby the line current induces an electromotive force in the rails of each track at points remote from said one vehicle and which electromotive force causes current to flow in the rails of all the tracks in multiple, and receiving apparatus located on a second vehicle of the train remote from said one vehicle including a signaling device responsive to such communication current and an inductor, and said inductor mounted on the vehicle to link the magnetic field due to the communication current flowing in the several rails in multiple for actuating the signaling device by the additive effect of the current in the several rails.

21. A railway communication system comprising transmitting apparatus located on one vehicle of a train and including a current source and a sending circuit efiectively coupled to the track rails 'to cause a communication current of a given frequency to'flow in the rails in multiple in both directions from the vehicle, receiving apparatus located on another vehicle of the train spaced apart from said one vehicle and including a signaling device responsive to said communication current and an inductor effectively coupled with the track rails for receiving an electromotive force due to communication current flowing in the rails at said other vehicle, a line wire disposed along the railway in inductive relation with the track rails for receiving an electromotive force due to the current in the rails at said one vehicle and to induce an electromotive force in the rails at said other vehicle due to communication current flowing in the line wire, and a plurality of tuning devices connected with said line wire and ground one at each of a plurality of selected locations and each including capacitance effective for reducing the characteristic. impedance of said line wire at the given frequency of the communication current.

22. A railway communication system comprising, transmitting apparatus located on one vehicle of a train and including a current source and a sending circuit eifectively coupled to the track rails to cause' a communication current of a given frequency to flow in the rails in multiple in both directions from the vehicle, receiving ap paratus iocated'on another vehicle of the train spaced apart from said one vehicle and including a signaling device responsive to said communication current and an inductor effectively coupled with thetrack rails for receiving an lelectromotive force due to communication current flowing in the rails at said other vehicle, a line wire disposed along the railway in inductive relation with the track rails for receiving an electromotive force due to the current in the rails at said one vehicle and to induce an electromotive force in the rails at said other vehicle due to communication current flowing in the line wire, and tuning devices connected with the line wire and ground at substantially equal spaced intervals to divide the line wire into consecutive sections and each of said devices including capacitance effective to establish a predetermined characteristic impedance and propagation constant for the line. wire at the frequency of the communication current.

23. A railway communication system comprising, transmitting apparatus located on one vehicle of a train and-including a current source and a sending circuit effectively coupled to the track rails to cause a communication current of a given frequency to flow in the rails in multiple in both directions from the vehicle, receiving apparatus located on another vehicle of the train spaced apart from said one vehicle and includcommunication current and an inductor effectively coupled with the track rails for receiving an electromotive force due to communication current flowing in the rails at said other vehicle, a line wire disposed along the railway in inductive relation with the track rails for receiving an electromotive force due to the current in the rails at said one vehicle andtoinduce an electromotive force in the rails at said other vehicle due to communication current flowing in the line wire, and tuning devices connected with the line wire and ground at substantially equal spaced intervals to divide the line wire into consecutive sections and each of said devices including capacitance and conductance effective to reduce the characteristic impedance of the line wire at said given frequency whereby the flow of communication current in the line wire is increased. 24. A railway communication system comprising, transmitting apparatus located on one vehicle of a train and including a current source anda sending circuit eflectively coupled to the track rails to cause a communication current of a given frequency to flow in the rails in multiple in both directions from the vehicle, receiving apparatus located on another vehicle of the train spaced apart from said one vehicle and including a signaling device responsive to said communication current and an inductor effectively coupled with the track rails for receiving an electromotive force due to communication current flowing in the rails at saidother vehicle, a line wire disposed along the railway in inductive-relation with the track rails for receiving an electromotive force due to the current in the rails at said one vehicle and to induce an-electromotiveforce in the rails at said other vehicle due to communication current flowing in the line wire, and a plurality of tuning devices associatedwith said line wire one at each of a plurality of selected points and said devices each including 'reactance proportioned to compensate the reactance of said line wire at said given frequency for establishing a low characteristic impedance of the line wire for the communication current.

25. A railway communication system comprismultiple in both directions from the vehicle, re-

ceiving apparatus located on another vehicle of the train spaced apart'from said one vehicle and including a signaling device responsive to said communication current and an inductor effectively coupled with the track rails for receiving an electromotive force due to communication current flowing in the rails at said other vehicle, a line wire disposed along the railway in inductive relation with the track rails for receiving an electromotive force due to the current in the rails atsaid one vehicle and to in-' v duce an electromotive force in the rails at said other vehicle due to communication current flowing in the line wire, and means connected with the line wire and ground and including reactance proportioned to compensate the reactance of said line wire at said given frequency for establishing a predetermined characteristic impedance of the line for the communication current. I

2e. Incombination. wan mum train-carried communication equipment including transmitting apparatus located on a vehicle of a train and capable of delivering a'communication current to a pair of output terminals, means to connect one of the: output terminals with the journal bearing of al wheel at one end of the vehicle, a return conductor disposed lengthwise along the top of the'vehicle, means including a vertical conductor at said one end of the vehicle to connect said return conductor with the other of said output terminals, and means including a vertical conductor at the opposite end of the vehicle to connect said return conductor'with the journal bearing of a wheel at said opposite end of the vehicle whereby said current is caused to flow in the track rails between said wheels.

27. In combination with railway train-carried communication equipment including transmitting apparatus located on a vehicle of a train and capable of delivering a carrier frequency communication current to a pair of output terminals, means to connect the journal bearings of a pair of wheels at one end of the vehicle in parallel with one of said output terminals, a return conductor disposed lengthwise along the top of the vehicle, means including a vertical conductor at. said one end of the vehicle to connect said return conductor with the other of said output. terminals, and means including a vertical conductor at the opposite end of the vehicle to connect the journal bearings of' a. pair of wheels at said opposite end in parallel with said return conductor whereby said current is caused to flow in the two rails between said two pair of wheels in parallel.

28. In combination with railway train-carried communication equipment including transmitting apparatus located on a vehicle of a train and capable of delivering a carrier frequency communication current to a pair of output terminals, means to connect a pair of wheels at one end of the vehicle in parallel with'one of said output terminals, a return conductor disposed lengthwise along the top of the vehicle, means including a vertical conductor at said one end of the vehicle to connect said return conductor with the other of said output terminals, and means including a vertical conductor at the opposite end of the vehicle to connect a pair of wheels at said opposite end inparallel with said return conductor whereby said current is caused to flow in the two rails between the two pair of wheels in parallel and inductive reactance of the rails is relatively high.

29; In combination with railway train-carried communication equipment including transmitting apparatus located on a vehicle of a train and capable of delivering a carrier frequency communication current to a pair of output terminals, means to connect the journal bearings of a pair of wheels at one end of the vehicle in parallel with one of said output terminals, a return conductor disposed lengthwise along the vehicle and relatively high above the top of the rails, means to connect one end of said return conductor with the other of said output terminals, other means to connect the journal bearings of a pair of wheels at the other end of the vehicle in parallel with the other end of said return conductor, and means to insulate each of said journal bearings from its associated journalbcx.

30. In combination with railway train-carried communication equipment including transmitting apparatus located on a vehicle of a train and capable of delivering an alternating communication current to the primary winding of an output transformer; a sending circuit on said veh'icle comprising a first conductor disposed lengthwise along the top of the vehicle, a second conductor disposed substantially vertical from a journal bearing of a wheel at one end of the vehicle to said first conductor and a third conductor disposed substantially vertical from a journal bearing of a wheel at the other end of the vehicle to said first conductor; and means to interpose the secondary winding of the output transformer in said second conductor.

31. In combination with railway train-carried communication equipment comprising, transmitting apparatus ona vehicle of a train capable of delivering an alternating communication current and including a sending circuit consisting of a return portion disposed lengthwise along the top of the vehicle and vertical portions at each end of the vehicle to connect with vehicle wheels one at each end, receiving apparatus responsive to such communication current and including an inductor mounted on the vehicle above the vehicle body and in a vertical plane to link a horizontal magnetic field transverse to the'track rails, and circuit means operative to selectively render said transmitting apparatus and said receiving apparatus active.

PAUL N. BOSSART. 

